Polishing pad for a chemical mechanical planarization or polishing (CMP) system

ABSTRACT

A polishing pad for a chemical mechanical planarization or polishing (CMP) system has a polish rate responsive to the pad contact area and the pad contact dynamics. The pad contact area is characterized by a predetermined statistical distribution. The pad contact dynamics are characterized by a mechanical behavior.

FIELD OF THE INVENTION

[0001] This invention generally relates to polishing systems forelectronic materials. More particularly, this invention relates topolishing pads for chemical mechanical polishing (CMP) systems.

BACKGROUND

[0002] Many manufacturers use a chemical mechanical polishing orplanarization (CMP) process to produce electronic materials such assemiconductors, integrated circuits, and the like. In a typical CMPprocess, a wafer is polished to produce an essentially level or smooth(planarized) surface at a microscopic level. The planarized surfaceassists manufacturers in meeting depth-of-focus and other limitations inlithography processes. The wafer can be an oxide or other dielectric, ametal, a semiconductor, a polymer or combination thereof

[0003] During operation of the CMP process, the surface of the wafer tobe polished is positioned against a platen, which has a polishing padfacing the wafer. The wafer and the polishing pad usually rotate in thesame direction while a polishing slurry is dispensed between the waferand the polishing pad. The polishing slurry usually is a colloidalsilica or other alkali-based solution for an oxide. The polishing slurryusually is an acid-based solution for a metal.

[0004] The surface topography of the wafer is reduced by a combinationof mechanical and chemical action of the polishing pad and polishingslurry against the surface of the wafer. Along the surface, the materialat the highest positions typically experiences the largest appliedpressure and is polished faster than material at lower positions. Thedifference in polish rates between the highest and lowest positionsresults in the planarization of the wafer surface.

[0005] The polish rate of the CMP process typically is sensitive to thesurface of the polishing pad. The polish rate tends to decay from aninitial maximum value as the pad surface is damaged by the polishingprocess. A conditioner device often is used to refresh or maintain thepolishing pad surface and thus slow or reverse the decay of the polishrate. The conditioner usually has a diamond coated or similar surfacefor removing material from the polishing pad. The quantification andcorrelation of polishing pad surfaces to polishing performance often isdifficult to ascertain. Some approaches use standard surface statisticssuch as roughness (Ra and Rms), skew, and kurtosis to estimate orpredict polishing performance based on pad surface statistics. However,these parameters usually have limited correlation to the polishingperformance, especially in oxide polishing. These parameters typicallydescribe the entire pad surface. Some CMP processes, notably oxidepolishing processes, are typically influenced primarily by changes inthe pad-wafer contact area or the near surface region of the polishingpad. In these cases, statistics describing the entire surface of the padhave limited utility. Other approaches correlate the average asperity orroughness of the near surface region to the polishing performance.

BRIEF SUMMARY

[0006] This invention provides a chemical mechanical planarization orpolishing (CMP) system having a polishing pad with a polish rateresponsive to the pad contact area and the mechanical behavior of thepolishing pad.

[0007] In one aspect, a polishing pad for a CMP system has a surfacecharacterized by a polish rate. The polish rate is responsive to a padcontact area and pad contact dynamics. The pad contact area ischaracterized by a predetermined statistical distribution of a padsurface height. The pad contact dynamics are characterized by themechanical behavior of the polishing pad.

[0008] In another aspect, a polishing pad for a (CMP) system has asurface characterized by a polish rate. The polish rate is responsive toa statistical distribution of a pad surface height and the mechanicalbehavior of the polishing pad. The statistical distribution includes afirst statistical distribution and a second statistical distribution.The first statistical distribution represents a bulk component of thesurface. The second statistical distribution represents a near surfacecomponent of the surface. The mechanical behavior of the polishing padmay be described by a full visco-elastic model, or may be approximatedas an elastic spring.

[0009] In a further aspect, a CMP system has a polishing pad, a platen,a wafer, a holder, and a slurry. The polish pad is disposed on theplaten. The wafer is mounted in the holder. The slurry is disposedbetween the polish pad and the wafer. The holder is operable to pressthe wafer against a surface of the polishing pad. The pad ischaracterized by a preferred statistical distribution of a pad surfaceheight and the mechanical behavior of the polishing pad. The polishingpad has a polish rate responsive to the pad surface height distributionand the mechanical behavior of the polishing pad.

[0010] Other systems, methods, features, and advantages of the inventionwill be or will become apparent to one skilled in the art uponexamination of the following figures and detailed description. All suchadditional systems, methods, features, and advantages are intended to beincluded within this description, within the scope of the invention, andprotected by the accompanying claims.

BRIEF DESCRIPTION OF THE FIGURES

[0011] The invention will be better understood with reference to thefollowing figures and detailed description. The components in thefigures are not necessarily to scale, emphasis being placed uponillustrating the principles of the invention. Moreover, like referencenumerals in the figures designate corresponding parts throughout thedifferent views.

[0012]FIG. 1 illustrates a CMP system according to an embodiment;

[0013]FIG. 2 illustrates a top view of the polishing pad in the CMPsystem of FIG. 1 according to one embodiment;

[0014]FIGS. 3A and 3B are plots in accordance with the inventionillustrating two-dimensional pad surfaces and corresponding pad heighthistograms of the polishing pad in FIG. 2; in which, FIG. 3A illustratesthe polishing pad after a break-in period, and FIG. 3B illustrates apolishing pad after polishing with no conditioning;

[0015]FIG. 4 is a plot illustrating a fitting procedure for analyzingthe pad height histogram data of a polishing pad in accordance with theinvention;

[0016]FIG. 5 is a plot illustrating a pad height histrogram and acorresponding cumulative pad volume of a polishing pad in accordancewith the invention;

[0017]FIGS. 6A, 6B, and 6C are plots illustrating pad surface parametersin accordance with the invention having a statistical correlation withthe polish rate at about a 100% confidence level; in which, FIG. 6Aillustrates the correlation of the reciprocal of the contact area withthe polish rate; FIG. 6B illustrates the correlation of the contact areawith the polish rate; and FIG. 6C illustrates the correlation of thearea fraction of the second peak with the polish rate;

[0018]FIG. 7A is a plot in accordance with the invention illustrating acorrelation according to the invention between the predicted contactarea and the polish rate of a polishing pad in a CMP system fordifferent polishing slurries with the same conditioning disc;

[0019]FIG. 7B is a plot in accordance with the invention illustrating acorrelation according to the invention between the predicted contactarea and the polish rate of a polishing pad in a CMP system for the samepolishing slurry and different conditioning discs;

[0020]FIG. 7C is a plot in accordance with the invention illustratingpolishing rate as s function of predicted pad contact area; and

[0021]FIGS. 8A and 8B are plots in accordance with the inventionillustrating a reduced polish rate in an oxide polishing process as afunction of a frictional loading factor FIG. 8A and the Sommerfeldnumber FIG. 8B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0022]FIG. 1 illustrates a CMP system 100 according to an embodiment ofthe invention. The CMP system 100 has a platen 102, a polishing pad 104,a wafer 106, a holder 108, a polishing slurry 110, and a pad conditioner112. The platen 102 holds and provides structural support for thepolishing pad 104. The holder 108 carries and presses the wafer 106against the polishing pad 104. During operation, the platen 102 andholder 108 rotate. The platen 102 rotates in the range of about 0 rpmthrough about 150 rpm. The holder 108 also rotates in the range of about0 rpm through about 150 rpm. The platen 102 and holder 108 can rotate atother speeds. The rotation speeds of the platen and holder need not beequal. The rotating wafer 106 presses against the rotating polishing pad104 while the polishing slurry 110 is dispensed between the wafer 106and the polishing pad 104. The applied pressure between the wafer 106and the polishing pad 104 is in the range of about 0-15 psi. Otherpressures can be used. The CMP system 100 can have other configurationsand arrangements including those with fewer and additional componentsand those with other or different process parameters.

[0023] The polishing pad 104 is a rigid, microporous polyurethane-basedpad such as the Rodel® IC1000 CMP Pad from Rodel, Inc. of Phoenix, Ariz.To fabricate the polishing pad, any prepolymer chemistry can be used inaccordance with the present invention, including polymer systems otherthan urethanes, provided the final product exhibits the followingproperties: a density of greater than about 0.5 g/cm³, more preferablygreater than about 0.7 g/cm³ and yet more preferably greater than about0.9 g/cm³; a tensile modulus of about 0.02 to about 5 GigaPascals;hardness of about 25 to about 80 Shore D; a yield stress of about 300 toabout 6000 psi; a tensile strength of about 500 to about 15,000 psi, andan elongation to break up to about 500%. These properties are possiblefor a number of materials useful in extrusion and similar-typeprocesses, such as: polycarbonate, polysulphone, nylon, ethylenecopolymers, polyethers, polyesters, polyether-polyester copolymers,acrylic polymers, polymethyl methacrylate, polyvinyl chloride,polycarbonate, polyethylene copolymers, polyethylene imine,polyurethanes, polyether imide, polyketones, and the like, includingphotochemical reactive derivatives thereof.

[0024] In one embodiment, the pad matrix is derived from at least oneof: an acrylated urethane; an acrylated epoxy; an ethylenicallyunsaturated organic compound having a carboxyl, benzyl, or amidefunctionality; an aminoplast derivative having a pendant unsaturatedcarbonyl group; an isocyanurate derivative having at least one pendantacrylate group; a vinyl ether, a urethane; a polyacrylamide; anethylene/ester copolymer or an acid derivative thereof; a polyvinylalcohol; a polyrnethyl methacrylate; a polysulfone; an polyamide; apolycarbonate; a polyvinyl chloride; an epoxy; a copolymer of the above;or a combination thereof. Preferred pad materials comprise urethane,carbonate, amide, sulfone, vinyl chloride, acrylate, methacrylate, vinylalcohol, ester or acrylamide moieties. The pad material can be porous ornon-porous. In one embodiment, the matrix is non-porous; in anotherembodiment, the matrix is non-porous and free of fiber reinforcement.The pad material may also contain abrasives. The polishing pad 104 caninclude other materials and can have other configurations includingthose with other or different process parameters. Polishing pads havingthe above material characteristics are also described incommonly-assigned, U.S. Pat. No. 6,287,185, which is incorporated byreference herein.

[0025] The pad conditioner 112 presses against and sweeps radiallyacross the polishing pad 104 during operation of the CMP system 100. Thepad conditioner 112 has a diamond-covered conditioning surface such asthe DiaGrid® brand Pad Conditioner available from Rodel, Inc. ofPhoenix, Ariz. The conditioning surface regenerates or refreshes the topsurface by removing pad material to create more asperities in thepolishing pad 104. The asperities created by the pad conditioner 112 canhave different shapes such as spherical, non-spherical, arbitrary, and acombination thereof. The pad conditioner 112 has a density of diamondson the conditioning surface in the range of about 1/mm² through about100/mm². The nominal size of individual diamonds on the conditionersurface is in the range of about 20 micrometers (μm) through about 500μm. The diamond crystal type can be varied over a range including,angular, blocky, mosaic and cubo-octahedral shapes. The pad conditioner112 has a pad removal rate in the range of about 0 μm/hour through about500 μm/hour of conditioning time. The conditioner has an applied load inthe range of about 0 lbs through about 50 lbs on the polishing pad 104.Other pad conditioners can be used including those with different orother process parameters.

[0026] The wafer 106 includes an electronic material such as asemiconductor, an integrated circuit, and the like. In one aspect, thewafer 106 includes an oxide. In another aspect, the wafer 106 includes ametal or alloy. In a further aspect, the wafer 106 includes an oxidewith a metal layer such as silicon dioxide with a tungsten layer. In afurther aspect the wafer 106 includes a oxide or low-k dielectricmaterial with a copper layer. The wafer 106 can include one or more ofSi, SiO₂, Cu, Ta, TaN, W, GaAs, TiN, Ti, Si₃N₄, and the like. The wafermay be composed other materials than those listed here.

[0027] The polishing slurry 110 can be a colloidal silica or otheralkali-based solution such as Rodel® ILD1300, KLEBOSOL®, or acombination thereof. The Rodel® ILD1300 slurry can be obtained throughRodel, Inc. of Phoenix Ariz. The KLEBOSOL® slurry can be obtainedthrough Clariant Corporation of Charlotte, N.C. The polishing slurry 110can include other etchant solutions and combinations includingacid-based solutions. Alternatively, the polishing solution can be areactive liquid composition that does not contain an abrasive component.

[0028] The surface of the wafer 106 is planarized or polished by themechanical friction and chemical etching of the polishing pad 104 andthe polishing slurry 110. The polish rate of the polishing pad 104 isresponsive to the pad contact area and the contact dynamics of thepolishing pad 104 with the wafer 106. As described below, the padsurface area can be characterized by a statistical representation of thepad surface. The pad contact dynamics can be ascertained from padsurface height statistics and the mechanical behavior of the polishingpad 104, the properties of the polishing slurry, and the processconditions. The pad surface data is analyzed by fitting a pad heighthistogram with one or more Gaussian or modified Gaussian components. Thepad height histogram represents the distribution of asperities on thepad surface. The subtle differences or localized differences in the padsurface can be assessed quantitatively. The components of the fit can bedescribed with a small set of parameters, which correlate with polishperformance. The mechanical behavior of the pad can be described bymodeling the volumetric displacement of the pad as an elastic spring.Other elastic or visco-elastic models for the pad mechanical behaviorcan be used. The pad contact area and the contact dynamics can be usedto obtain or determine an optimal polish rate for the polishing pad 104.In one aspect, the optimal polish rate corresponds to rate-saturatedconditioning, where the regeneration of the pad surface by theconditioner is about equal to the deformation of pad asperities by thewafer. The optimal polish rate can correspond to other contact dynamicsand contact area parameters between the polishing pad 104 and the wafer106.

[0029]FIG. 2 represents a top view of the polishing pad 104 in the CMPsystem 100 according to one embodiment. The polishing pad 104 has a topsurface 120 including a non-contact portion 122 and a contact track orpath 124. The wafer 106 does not contact the polishing pad 104 on thenon-contact portion 122 during operation of the CMP system 100. Thewafer 106 contacts the polishing pad 104 at a pad-wafer contact area126, which follows the contact track or path 124 during operation of theCMP system 100. The top surface 120 has a surface texture or morphology.The top surface 120 can have other configurations and arrangementsincluding other or different non-contact portions and contact tracks orpaths.

[0030] The surface texture or morphology of the top surface 120 ischaracterized by asperities, which are the variations in the pad heightalong the top surface. The asperities are initially present in thepolishing pad 104 and can be created by the conditioner 112 prior to orduring operation of the CMP system 100. The height of each asperity canbe measured in relation to a zero height position. The zero heightposition can be a geometric average of all the asperities, a singleasperity height such as the highest or lowest asperity, or some otherpredetermined level. The distribution of asperities is representedstatistically by a pad height histogram. The asperities can have one ormore shapes including spherical, non-spherical, and arbitrary shapes.

[0031] The pad surface texture is analyzed to determine the pad surfacecontact area and other data associated with the pad contact dynamics.The pad surface texture can be analyzed initially to provide set-pointor standard data for a given type of polishing pad 104. These set-pointdata would be available to determine the optimal polish rate of thepolishing pad 104 under various operating conditions of the CMP system100. The pad surface texture also can be analyzed during operation ofthe CMP system 100 to establish or update the data.

[0032] The pad surface texture is analyzed using a vertically scanninginterference microscope such as the WYKO NT3300 from Veeco Instruments,Inc. of Woodbury, N.Y. Other interference microscopes or other surfacetexture measurement devices can be used. The pad surface texture ischaracterized using various statistics such as standard roughnessparameters and a height histogram peak fitting procedure outlined below.In one aspect, the pad surface feature is measured using multipleazimuthal or radial locations on the pad for a given time interval. Inaddition to standard roughness parameters, pad surface texturestatistics are analyzed using the peak fitting procedure.

[0033]FIGS. 3A and 3B represent two-dimensional pad surfaces andcorresponding pad height histograms of the polishing pad in FIG. 2. Thetwo-dimensional pad surfaces are taken from line scans of thethree-dimensional pad surface data from the contact track or path 124 ofthe polishing pad 104. FIG. 3A represents a polishing pad after abreak-in period. FIG. 3B represents a polishing pad after about 31minutes of polishing with no conditioning. The pad height histogramshave been rotated 90° to correspond to the pad-height axis of the padcross-sections. FIGS. 3A and 3B illustrate a qualitative picture of thephysical implications of the height histogram data. In FIG. 3A, the postbreak-in surface is not deformed by pad-wafer contact and exhibits asmooth, tailed Gaussian distribution of pad surface height. In FIG. 3B,prolonged pad-wafer contact, especially in the absence of conditioning,results in a pad with a flattened surface. In the pad-height data, thiscorresponds to the emergence of a secondary mode in the histogram nearthe pad surface.

[0034]FIG. 4 illustrates a fitting procedure for analyzing the padheight histogram data of a polishing pad. The histogram shows pointfrequency as a function of pad-height. The designation of zero height isbased on the geometric average of the data set. The height distributionhas been fitted with a two-component system consisting of two distinctGaussian or exponentially modified Gaussian contributions. Theasperities not in contact with the wafer represent a primary (bulk)component of the pad surface and are described by an exponentiallymodified Gaussian (EMG) distribution. The “as-conditioned” surface ofthe polishing pad can be described by a similar distribution as the bulkcomponent. An EMG distribution can be thought of as a Gaussiandistribution with a superimposed exponential “tail”. The asperities incontact or near to contact with the wafer represent a secondary (nearsurface) component of the pad surface and are described by either aGaussian or EMG distribution. This combination of Gaussian and EMGdistributions provides a system that captures a majority of thedistribution behavior of contact and non-contact areas for a wide rangeof data sets.

[0035] A Gaussian and EMG combination is useful in situations where thesecondary component can not exhibit a distinct maximum. In these cases,a secondary component represented as an EMG can exhibit severe tailingby attempting to minimize the overall error of the fit whereas asecondary component represent as Gaussian will not. In a CMP systemusing an IC1000 polishing pad, a ILD1300 polishing slurry, and acubic-octahedral conditioner, a distinct secondary maximum is observedin the histogram and therefore the tail of the distribution can beadjusted on both the primary and secondary components to obtain asatisfactory fit. The tendency of the secondary component to exhibit asevere tail can be statistically limited by the slope of the secondarymaximum. Other combinations of statistical distributions, specificallyPearson distributions or modified Gaussian distributions with additionaladjustable parameters, can be used and, in some cases, can be moreeffective at capturing the pad height histogram distribution. However,as the number of adjustable parameters increases, the statisticalability to attach physical significance to those parameters decreases.

[0036] The Gaussian distribution can be described mathematicallyaccording to Equation 1 as follows: $\begin{matrix}{{y = {a_{0}{\exp \left\lbrack {{- \frac{1}{2}}\left( \frac{x - a_{1}}{a_{2}} \right)^{2}} \right\rbrack}}},} & (1)\end{matrix}$

[0037] where the constants a₀, a₁, and a₂ refer to the amplitude,center, and width of the standard deviation.

[0038] The EMG distribution can be described mathematically according toEquation 2 as follows: $\begin{matrix}{{y = {\frac{a_{0}}{2\quad a_{3}}{{\exp \left( {\frac{a_{2}^{2}}{2a_{3}^{2}} + \frac{a_{1} - x}{a_{3}}} \right)}\left\lbrack {{{erf}\left( {\frac{x - a_{1}}{\sqrt{2\quad}a_{2}} - \frac{a_{2}}{\sqrt{2}a_{3}}} \right)} + \frac{a_{3}}{a_{3}}} \right\rbrack}}},} & (2)\end{matrix}$

[0039] where a1 and a2 represent the center and width of de-convolvedGaussian contribution to the overall peak, which is defined asGauss(a₀,a₁,a₂){circle over (x)}Exp(a₃), and where a₃ is the timeconstant of the exponential contribution.

[0040] Based on the fitting results, the height histogram data can bedescribed with a handful of parameters as previously discussed. The peakfit results can be obtained using non-linear curve fitting software suchas the PeakFit® software package from SPSS Science in Chicago, Ill.Other curve fitting software and procedures can be used.

[0041] The contact dynamics are responsive to the mechanical behavior ofthe polishing pad 104. The pad-wafer contact area can be estimated usingan elastic model for the mechanical behavior of the polishing pad 104.Hooke's Law provides the elastic model according to Equation 3 asfollows: $\begin{matrix}{{\sigma = {k\frac{\Delta \quad l}{l}}},} & (3)\end{matrix}$

[0042] where σ is the stress, k is an effective spring constant of thepolishing pad 104, l is the length or thickness of the polishing pad104, and Δl is the change in length or deflection of the polishing pad104.

[0043] The effective spring constant of an IC1000 pad is about 4.5×10⁸Pa. Using Hooke's Law, a 62 kPa stress on the pad yields a paddeflection of about 0.135 μm. A wafer pressure of about 9 psi canprovide the 62 kPa stress on the pad. Over a 1800×2400 μm area, which isa scan area for the pad analysis, the pad deflection would result in adisplaced pad volume of about 5.8×10⁵ μm³. Other scan areas can beanalyzed. While Hooke's Law is used as the elastic pad model, any otherelastic or visco-elastic model of the pad mechanical behavior can beused. In one aspect, the pad model incorporates a more accuratedescription of the pad visco-elastic behavior. In another aspect, thepad model incorporates x-y pad “asperity” distributions as well as thez-distributions already considered.

[0044] Numerical integration of the pad height histogram yields acumulative pad displaced volume as a function of pad height. Thenumerical integration to determine the displaced pad volume can beperformed according to Equation 4, as follows: $\begin{matrix}{{V + {\sum\limits_{i = 1}^{b}\left\lbrack {h_{i}A_{p}{\sum\limits_{i = 1}^{b}n_{i}}} \right\rbrack}},} & (4)\end{matrix}$

[0045] where the pad height histogram is divided into “b” bins withn_(i) points or pixels in each bin, where A_(p) is the area associatedwith each discrete point (or pixel) in the scan, and where h_(i) is thez-height of the bin.

[0046] The bins are numbered consecutively starting with the highestpoint in the scan and moving down through the pad. Comparison of thepredicted displaced volume with the calculated pad volume yields anestimate of the depth of wafer penetration into the pad and also thecontact area between the wafer and the pad. This procedure representsthe numerical equivalent of pressing the wafer 106 into the polishingpad 104 and quantifying the area of pad in contact with the wafer.

[0047]FIG. 5 illustrates a pad height histogram and a correspondingcumulative pad volume of a polishing pad. The point at which thepredicted displaced volume is about equal to the cumulative pad volumeis shown. The pad has a predicted contact area of about 10.4%, whichcorresponds to a pad height of 7.3 μm.

[0048]FIGS. 6A, 6B, and 6C illustrate pad surface parameters having astatistical correlation with the polish rate at about a 100% confidencelevel. FIG. 6A illustrates the correlation of the reciprocal of thecontact area with the polish rate. FIG. 6B illustrates the correlationof the contact area with the polish rate. FIG. 6C illustrates thecorrelation of the area fraction of the second peak with the polishrate. The correlation of these pad surface parameters, especially thereciprocal contact area which (given a constant applied force to thewafer) represents a mean asperity pressure, indicates the asperitycontact mechanism underlying the cause of polish rate decay. In oneaspect, the pad surface parameters are from a CMP system using ILD1300slurry and an IC1000 pad. Other CMP systems can provide similarconfidence levels for similar parameters. Other pad surface parametersalso can have a strong correlation with the polish rate. Some padsurface parameters can not have a strong correlation with the polishrate. In one aspect, none of the standard roughness parameters arestrongly correlated with the polish rate.

[0049]FIG. 7A illustrates a correlation between the predicted contactarea and the polish rate of a polishing pad in a CMP system. The datashow the results of several polishing slurries when used with an IC1000polishing pad. The data in FIG. 7A was generated by first achieving asteady state polish rate with pad conditioning, and then suspending padconditioning and tracking the resulting evolution of both the polishrate and the corresponding pad surface state. Generally, predicted padcontact area always increases as a function of time without conditioningfrom a minimum steady state value. A single and consistent conditionerdesign was used to generate the data in FIG. 7A.

[0050] As indicated in FIG. 7A, polishing slurries ILD1300, and Rodel®ILD1300 J9 show an increase in the polish rate as the contact areadecreases. Conversely, polishing slurries Klebosol and a mixture ofKlebosol with ILD1300 show an increase in the polish rate as the contactarea increases up to about 6% contact area, a local maximum in rate ataround 6% contact area, and a decrease in rate above 6%.

[0051]FIG. 7B shows the results of multiple conditioners of varyingdesign on the correlation between predicted contact area and polish ratewhen using ILD1300 slurry. All of the data in FIG. 7B were generatedafter a steady state polish rate was achieved with conditioning, suchthat each data point in FIG. 7B represents a steady state value at anequivalent process condition with only the conditioner design beingvaried. A wide range of diamond crystal spacing (from 1/mm² to 3.3/mm²),diamond crystal size (from 150-210 μm) as well as diamond crystal types(angular, blocky, mosaic and cubo-octahedral) were evaluated in theseexperiments. The conditioners exhibiting more aggressiveness, asmeasured by the amount of pad material removed per unit time, result inpad surfaces with lower percent contact area. Accordingly, the design ofthe conditioner has a dramatic effect on the percent of pad area incontact with the wafer and also the polish rate.

[0052] In a preferred embodiment of the invention, the pad conditionercan have diamond crystal sizes ranging form about 20 microns to about500 microns. Also, the spatial density of diamond crystals can vary fromabout 1 to about 100 per square millimeter. Further, the pad conditioneris configured such that the removal rate of pad material ranges fromabout 0 microns per hour to about 200 microns per hour.

[0053]FIG. 7C illustrates polish rate versus contact area for multipleconditioners of varying design on the correlation between predictedcontact area and polish rate when using ILD1300 slurry and a Rodel®OXP4000 polishing pad. The data in FIG. 7C was generated by firstachieving a steady state polish rate with pad conditioning, and thensuspending pad conditioning and tracking the resulting evolution of boththe polish rate and the corresponding pad surface state. As in the caseof the data in FIGS. 7A and 7B, the data in FIG. 7C exhibit a maximum inpolish rate. In this case, the maximum is present at around 3.5% padcontact area. Since the process conditions in this run were identical tothose used in FIGS. 7A and 7B, the primary difference is the mechanicalproperties of IC1000 pad versus OXP4000 pad. This example serves toillustrate the potential variations in polish rate maxima as a functionof pad mechanical properties.

[0054] In a one embodiment, the polish rate has a maximum within a rangeof about 0% to about 15% pad contact area. In another embodiment, thepolish rate has a maximum within a range of about 3% to about 8% padcontact area. In yet another embodiment, the polish rate has a maximumat about 6% pad contact area. In a further embodiment, the polish ratehas a maximum at about 3.5% pad contact area. The optimal pad-wafersurface contact area varies depending on process conditions, such as padproperties, slurry, wafer type, platen and carrier speeds, and the like.The optimal pad-wafer surface contact area also varies depending on thepad physical properties. Other methods of calculating pad contact areamay yield a different estimate for the same process conditions and padsurface statistics.

[0055] Two competing processes determine the pad surface texture. Thepad conditioner 112 operates to maintain a nearly normal distribution ofpad heights through the constant removal of pad material andregeneration of the pad surface. The pressure of the wafer against thepad surface results in plastic deformation of the near surface padasperities and a blunted pad surface height distribution. The amount ofpad surface in contact with the wafer is highly dependent on the padheight distribution, which can be visualized by comparing extreme casesof a pad asperity such a square cross-section with a conicalcross-section. For equivalent small volume displacements, the squareasperity exhibits a higher contact area than the conical asperity.

[0056] By analogy and supported by the elastic model applied to the padheight distribution data, the as-conditioned pad surface also exhibits alower predicted pad contact area. The pad-wafer contact shifts the padheight distribution towards more pad area in contact with the wafer. Theslurry type can have a large effect on this interaction, with colloidalslurries exhibiting minimal pad distortion and fumed silica slurriesexhibiting more pad surface distortion. While the pad surface area incontact with the wafer is determined by the slurry type, the polish rateappears to be independent of slurry type and determined primarily by padcontact area. There is an optimal amount of pad surface contact thatcorresponds to a maximum polish rate for the system. Below this optimalcontact area, polish rate drops and tends towards zero rate for zeroarea in contact. Above this optimal level, the polish rate drops withincreasing contact area. In a low contact area regime, the polish ratecan be limited by the fact that a limited number of point contacts existsuch that sufficient averaging cannot take place over the entire wafersurface. Above the optimal value, the polish rate can be limited by thedynamics of the pad wafer contact such as a reduction in mean contactpressure or some other effect. In one aspect, the optimal polish rate orrange can be characterized as “rate-saturated conditioning”. When thepad contact area is less than the optimal, the pad contact area can becharacterized as “over-saturated” conditioning. When the pad contactarea is more than the optimal, the pad contact area can be characterizedas “under-saturated” conditioning.

[0057] A dominant contributor to polish rate decay is conditioner wear.The conditioner wear could drive the process from a conditioningdominated state to more of a wafer dominated state with a subsequentloss in removal rate as the operating point shifts towards a higher padcontact area. The initial conditioner dominated process state is afunction of the slurry type, in that the slurry type has a largeinfluence on the degree to which the wafer-pad interaction causes padasperity “clipping”. The steady-state contact area can vary.

[0058] In one aspect, an in situ process with Klebosol 1501-50 has asteady-state contact area of about 4%. In another aspect, an ex situKlebosol process has a steady-state contact area of about 7%. In afurther aspect, an in situ process using ILD1300 exhibits a steady statecontact area of around 10%. In yet another aspect, fumed silica slurriesare not driven to a rate-saturated state, even with 100% in situconditioning. In yet a further aspect, with a more aggressiveconditioning process or a more aggressive conditioner design, theconditioner contribution can increase and the operating point can bedriven to a rate saturated state. In one more aspect, a conditioningcontrolled, rate-maximized process could be designed if the surfacemorphology that corresponds to an optimal polish rate could bedetermined. A conditioner could potentially be designed to result in adesired amount of asperity “clipping” to yield the optimal polish rate.When driven to a conditioning saturated operating point, a high ratecould be maintained, independent of the slurry type. Pad-aggressiveslurries (such as fumed silica) would have more aggressive conditioningto maintain the optimal surface.

[0059]FIGS. 8A and 8B illustrate the relationship between the polishrate (defined as the measured polish rate divided by the product ofwafer applied pressure and relative velocity between the wafer and pad)and a frictional loading factor (μV/P_(c)), FIG. 8A, and the Sommerfeldnumber (μVA_(c)/Pσ), FIG. 8B, where P is the applied pressure to thewafer, V is the relative velocity between the wafer and pad, A_(c) isthe area contact fraction between the wafer and pad, such that contactpressure P_(c) equals P/A_(c), μ is the slurry viscosity, and σ is acharacteristic length scale taken to be equivalent to the average padroughness, R_(a).

[0060] Those skilled in the art will recognize the Sommerfeld number asthe ratio of viscous to pressure forces. As illustrated in FIG. 8B,boundary lubrication, where the behavior at the pad wafer interfacewould be dominated by contact mechanics, occurs when S_(o) is less thanabout 1. Alternatively, mixed lubrication, where hydrodynamic effectsbecome significant, occurs in the range where S_(o) is greater thanabout 1 and less than about 3. In accordance with the invention, theSommerfeld number can ranges from about 0 to about 3.

[0061] In accordance with the invention, evaluation of frictionalloading factors and pressure forces enables the design of a polishingsystem to exploit the relative effects of a contact dominated or ahydrodynamically dominated system. Since the polish behavior resultingfrom the frictional forces at the pad-wafer interface is significantlydifferent in the opposing regimes, analysis and exploitation of thisbehavior provides a pad-slurry-process system with improved polishingcharacteristics.

[0062] Various embodiments of the invention have been described andillustrated. However, the description and illustrations are by way ofexample only. Other embodiments and implementations are possible withinthe scope of this invention and will be apparent to those of ordinaryskill in the art. Therefore, the invention is not limited to thespecific details, representative embodiments, and illustrated examplesin this description. Accordingly, the invention is not to be restrictedexcept in light as necessitated by the accompanying claims and theirequivalents.

1. A polishing pad for a chemical mechanical planarization (CMP) system,comprising: a surface characterized by a polish rate responsive to a padcontact area and pad contact dynamics, wherein the pad contact area ischaracterized by a predetermined statistical distribution of a padsurface height, and wherein the pad contact dynamics are characterizedby a mechanical behavior of the polishing pad.
 2. The polishing pad ofclaim 1, wherein the predetermined statistical distribution comprises asum of a first statistical distribution and a second statisticaldistribution.
 3. The polishing pad of claim 2, wherein the firststatistical distribution comprises a distribution based on a bulkcomponent of the surface, and wherein the second statisticaldistribution comprises a distribution based on a near surface componentof the surface.
 4. The polishing pad of claim 2, wherein the firststatistical distribution comprises an exponentially modified Gaussiandistribution, and wherein the second statistical distribution comprisesa Gaussian distribution.
 5. The polishing pad of claim 1, wherein thestatistical distribution comprises at least one mathematicaldistribution selected from the group consisting of a Gaussiandistribution, an exponentially modified Gaussian distribution, and aPearson distribution.
 6. The polishing pad of claim 1, wherein the padsurface height comprises surface height characterized by a pad heighthistogram.
 7. The polishing pad of claim 6, wherein the pad surfaceheight comprises a surface height responsive to a geometric average of asurface height data set.
 8. The polishing pad of claim 1, wherein themechanical behavior comprises behavior responsive to a volumetricdisplacement of the polishing pad.
 9. The polishing pad of claim 1,wherein the mechanical behavior comprises behavior comprises behaviorcharacterized as an elastic spring.
 10. The polishing pad of claim 1,wherein the mechanical behavior comprises behavior characterized byHooke's Law.
 11. The polishing pad of claim 1, wherein the polish ratecomprises a rate responsive to an optimal pad contact area.
 12. Thepolishing pad of claim 11, wherein the optimal pad contact areacomprises about 0 percent to about 15 percent.
 13. The polishing pad ofclaim 11, wherein the optimal pad contact area comprises about 3 percentto about 8 percent.
 14. The polishing pad of claim 11, wherein theoptimal pad contact area comprises about 6 percent.
 15. The polishingpad of claim 11, wherein the optimal pad contact area comprises an areathat varies in response to at least one process parameter.
 16. Thepolishing pad of claim 15, wherein the at least one process parametercomprises a slurry, a wafer type, a platen speed, and a holder speed.17. The polishing pad of claim 15, wherein the at least one processparameter comprises at least one physical property of the polishing pad.18. The polishing pad of claim 17, wherein the at least one physicalproperty comprises one or more of: i. a density greater than about 0.5g/cm.sup.3; ii. a tensile modulus of about 0.02 to about 5 GigaPascals;iii. a hardness of about 25 to about 80 Shore D; vi. a yield stress ofabout 300 to about 6000 psi; iv. a tensile strength of about 1000 toabout 15,000 psi; and v. an elongation to break up to about 500%.
 19. Apolishing pad for a chemical mechanical planarization (CMP) system,comprising: a surface characterized by a polish rate responsive to apredetermined statistical distribution of a pad surface height and amechanical behavior of the polishing pad, wherein the statisticaldistribution comprises a first statistical distribution and a secondstatistical distribution, the first statistical distributionrepresenting a bulk component of the surface the second statisticaldistribution representing a near surface component of the surface, andwherein the mechanical behavior is characterized by an elastic spring.20. The polishing pads of claim 19, wherein the first statisticaldistribution comprises an exponentially modified Gaussian distribution,and wherein the second statistical distribution comprises a Gaussiandistribution.
 21. The polishing pad of claim 19, wherein the statisticaldistribution comprises at least one mathematical distribution selectedfrom the group consisting of a Gaussian distribution, an exponentiallymodified Gaussian distribution, and a Pearson distribution.
 22. Thepolishing pad of claim 19, wherein the polish rate comprises a rateresponsive to an optimal pad contact area.
 23. The polishing pad ofclaim 22, wherein the optimal pad contact area comprises an area thatvaries in response to at least one process parameter.
 24. The polishingpad of claim 19, wherein the mechanical behavior comprises behaviorcharacterized by Hooke's Law.
 25. A chemical mechanical planarization(CMP) system, comprising: a polishing pad disposed on a platen; a wafermounted in a holder; and a slurry disposed between the polishing pad andthe wafer, wherein the holder is operable to press the wafer against asurface of the polishing pad, wherein the surface is characterized by apredetermined statistical distribution of a pad surface height and amechanical behavior of the polishing pad, and wherein the polishing padhas a polish rate responsive to the pad surface height distribution andthe mechanical behavior.
 26. The CMP system of claim 25, wherein thestatistical distribution comprises an exponentially modified Gaussiandistribution and a Gaussian distribution.
 27. The CMP system of Caim 25,wherein the mechanical behavior comprises behavior characterized byHooke's Law.
 28. The CMP system of claim 25, wherein the polish ratecomprises a rate responsive to an optimal pad contact area.
 29. The CMPsystem of claim 28, wherein the optimal pad contact area comprises about0 percent to about 15 percent.
 30. The CMP system of claim 25, whereinthe polishing pad comprises a thermoplastic material.
 31. The CMP systemof claim 30, wherein the thermoplastic material comprises at least onemoiety selected from the group consisting of a urethane; a carbonate; anamide; an ester; an ether; an acrylate; a methacrylate; an acrylic acid;a methacrylic acid; a sulphone; an acrylamide; a halide; and ahydroxide.
 32. The CMP system of claim 25, wherein the wafer comprisesat least one of an oxide, a metal, a semiconductor, and an alloy. 33.The CMP system of claim 25, wherein the wafer comprises at least one ofSi, SiO₂, GaAs, Cu, Ta, TaN, W, TiN, Ti, and Si₃N₄.
 34. The CMP systemof claim 25, wherein the slurry comprises one of an alkaline-basedsolution and an acid-based solution.
 35. The CMP system of claim 25,wherein the slurry comprises colloidal silica.
 36. The CMP system ofclaim 25 further comprising a pad conditioner disposed on the polishingpad, the pad conditioner operable to remove pad material from thepolishing pad.
 37. The CMP system of claim 36, wherein the polish ratecomprises a rate responsive to the removal of pad material by the padconditioner.
 38. The CMP system of claim 37, wherein the polish ratecomprises a rate characterized as rate-saturated conditioning.
 39. Apolishing pad for a chemical mechanical planarization (CMP) system,comprising: a surface characterized by a polish rate responsive to a padcontact area and pad contact dynamics, wherein the pad contact area ischaracterized by a predetermined statistical distribution of a padsurface height, and wherein the pad contact dynamics are characterizedby a frictional loading factor and a pressure force.
 40. The polishingpad of claim 39, wherein the pressure force is characterized by theSommerfeld number.
 41. The polishing pad of claim 40, wherein theSommerfeld number ranges from about 0 to about
 3. 42. The polishing padof claim 39, wherein the frictional loading factor is represented by theexpression μV/P_(c), where P_(c) is an applied pressure by the polishingpad to a wafer divided by the pad contact area, V is a relative velocitybetween the wafer and the polishing pad, and μ is a slurry viscosity.43. The polishing pad of claim 39, wherein the pad contact area isresponsive to pad conditioning of the surface by a pad conditioner. 44.The polishing pad of claim 43, wherein the pad conditioner comprises aconditioner having diamond crystals with a spatial density ranging fromabout 1 per square millimeter to about 100 per square millimeter. 45.The polishing pad of claim 44, wherein the diamond crystals comprisecrystals having geometric configurations selected from the groupconsisting of angular, block, mosaic, and cubo-octahedral.
 46. Thepolishing pad of claim 44, wherein the diamond crystals have nominaldiameters in the range of about 20 to about 500 μm.
 47. The polishingpad of claim 43, wherein the pad conditioner is characterized by a padmaterial removal rate of between about 0 to about 200 μm/hour.